Advice on pouring thin sections

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OddDuck
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Re: Advice on pouring thin sections

Post by OddDuck » Mon Jan 02, 2017 11:20 pm

Yep, and if you can't find sodium silicate locally (like up around here...) and you don't want to buy gallons of the stuff, check at a plumbing supply place and look for a product called "Boiler Weld". This is basically sodium silicate with some colloidal material added to seal up weeping or leaking boilers. I use this, it's about $10 for a quart, and works pretty slick. You may have to play around with sand/liquid ratios to get the results you want, I usually eyeball it. Doesn't stink if you need to bake it, either, and that is a god way to fairly quickly harden it without gassing it.
"If you took the bones out they wouldn't be crunchy!" -Monty Python's Flying Circus

jscarmozza
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Re: Advice on pouring thin sections

Post by jscarmozza » Tue Jan 03, 2017 2:22 pm

First, thanks for the tip off on the barbecue grill alloy, I wasn't aware it contained zinc, I did use it for a set of step pulleys that I made last summer and it did machine nicely, but I won't use it for this pour.

I attached a few pictures of the roof panel pattern and 3 of the 4 sand cores needed. You'll notice that I drilled a hole through the cores, I was planning on using that hole as the sprue, and carving the gates into the cores between each section. The rectangular notches in the bottom of the cores are for threaded rods to clamp the cores together. You'll also see a crows foot drawn on one of the cores, that will be the gate location. In a nutshell, once the mold is made up, I plan on pouring through the cores, the first gate being at the bottom (outside edge of the first core), the second gate will be 2-3/4" up the sprue between the first and second cores, the third gate 5-1/2" up the sprue between the second and third cores and the last gate 8-1/4" up, between the third and fourth cores. Along with a lot of venting, I'm hoping this will fill the mold quickly with hot enough metal to eliminate cold shuts. With this method I can't tilt the sprue as you suggested, I'll choke it a little above the first gate so the sprue fills and quiets the metal as it first enters the mold. Now, all that being said, do you think this is a good plan?

Finally, thanks for the tips on making cores. I started out making cores with molasses water and flour, then moved on to using linseed oil. I do have to say that I like the oil cores, they're tough after baking (drying), but they do stink up the house. I keep my molding sand in the garage, I checked last night and it was a little frosty; so I may not be able to pour this for a while.
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Roof pattern
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Cores

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steamin10
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Re: Advice on pouring thin sections

Post by steamin10 » Tue Jan 03, 2017 9:18 pm

Ok, the visual helps a lot. I will give my honest impressions shooting from the hip.

For the pattern, any thing that works is good. I see you want some rivet detail on the roof. ok, but that may cause problems on stripping on the near verticle sides. the rivets will hang up and cause tear out leaving grooves. I assume this is appropriate for a more modern loco, as early models had more flat roofs.

the reason I suggested one inch pouring sprue, is to get the volume up. That serves two purposes, of larger mass to retain heat, and more weight to push metal out the sprue bottom. this will go a long way to solving problems. Small sprues can be too light and freeze off early.

likewise chokes work against you slowing the movement, when rapid is what we want. So be carefull with restricting flow.

Since I am a hoarder, I use metal tubing from cheep brooms, for cut in tools, as they have thin walls, and are cheep. (throw aways) I use the wooden broom handles for dowels and runners in my molding, along with assorted toilet piping that is brass and thin wall. A piece of angle iron serves as a strike for the molding after compaction. While I have an air rammer, a rubber hammer, or hand tamper with double ends can be made for your molding. I dont know how far your equipment is developed.

Basically if you can get a clean strip on your pattern, go for it. You will learn if it fails, and get better.

On one occasion I made freight truck frames with aluminum. 12 pours without a hitch. the next day 8 pours, and only3 usable castings. For the life of me I dont know what happened. A mentor told me it was the iron cook pot getting the iron pasty, with the revert going into the melt. Once I began using the bad castings, the process stalled with the pasty metal not filling out. So beware of painting yourself into a corner.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
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jscarmozza
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Re: Advice on pouring thin sections

Post by jscarmozza » Wed Jan 04, 2017 9:01 am

The rivets may be a problem, even on the LE roof casting it looks like they had some problems and filed down the rivet heads as they got near the vertical edge. To reduce the possibility of tearing I used flat head brads and slopped on a few thick coats of finish to create a fillet around the heads, I also set the brad heads a little deeper as I got near the edge. Last night I brought a few buckets of casting sand into the basement from the garage to warm up so that I can do a trial run and see how everything fits together and if the pattern releases. I still haven't made the tilt up flask, after making the trial mold, I'll be better able to understand how things have to happen. I'm having a hard time visualizing this tilt-up method and everything involved.

Every Tuesday I take mom food shopping because she's 92 and I don't want her driving around. She doesn't want me to go in the store with her because she says I rush her, so while I was waiting in the parking lot I was reading Amman's book on sand casting. He made a comment about not letting the metal flow over a core. He didn't say why, but I think he meant that as the core burns out the sand becomes loose and washes into the mold. Now I'm wondering if my idea of pouring and gating through the core is a good idea. I'd like to hear your thoughts on this.

I'll post a few pictures of the trial mold, and we'll see how it looks. Thanks to all for taking the time to comment. John

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steamin10
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Re: Advice on pouring thin sections

Post by steamin10 » Wed Jan 04, 2017 10:31 am

Ammen is who is my guiding star with his various books. He is quite thorough and has been there.

Somewhere I meantiioned about pouring over or into a cavity, This is a fault that will carry sand into the cast. Cores are made to be hard, but break down with the heat of the cast, releasing the part, and there is the rub. A hot turbulent flow can erode any core. So it is a gentle rise inquuiet metal that we seek, and the breakdown happening after it steeps in the heat.

You are getting the idea of a bunch of rules, and that is some conditions to heed. remember to pay attention to what is, and not get lost in what you want it to be. You wont win that fight. think it through and act on it accordingly for success.

I will be absent from this forum for a bit, as an elder cousin has expired. That and regular activities are going to crowd my time. So I bid you godd luck, it is by your hand.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

jscarmozza
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Re: Advice on pouring thin sections

Post by jscarmozza » Thu Jan 05, 2017 7:25 pm

The test mold I rammed up, turned out well, the rivet impressions were all clean except for the ones along the edge they pulled the sand a little. My approach to this is probably wrong, but I'm going to see it through. I'm going to coat the core in a core wash to see if that will keep the core intact until the pour is complete. I'll let you know how that worked. John

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Re: Advice on pouring thin sections

Post by jscarmozza » Sun Jan 22, 2017 2:47 pm

The weather was pretty mild here in NJ for January so I poured yesterday and things went amazingly well. However, it was a learning experience making the mold, I made four attempts before getting it right. In the first try the core didn't fit the core print and pushed out the top of the mold; in the second try the threaded rods I used to hold the four cores together we're too long and gouged the sand cavity and set crooked in the core print; in the third try the bottom fell out of the flask when I picked it up. Let me tell you boys, I didn't handle any of them very well but the last one secured me a seat next to the pilot light of hell! I walked away from it for a few days and like Cool Hand Luke, I got my mind right. When I rammed up the last mold, I fastened the bottom board to the flasks with a few drywall screws, this prevented the sand from dropping out, I also enlisted my neighbor to help me close the mold. It was very heavy with not much play between the core and print. I moved into place, tilted it up on edge, opened the hinged side of the flask and was ready to pour. I poured a few other things first, leaving this until last so the crucible furnace was nice and hot, I used ingots that I had made previously so the metal was clean, I let this melt soak until my pyrometer read over 1500 degrees F and I poured fast. I really wasn't optimistic, but the mold took a lot of metal so I figured that I may of had something; much to my surprise, it turned out pretty well, not perfect, but pretty good. I didn't clean it up yet so I'm not sure how well all of the rivets came out, I'm going to do that tomorrow. I attached a few photos, front and back, the metal spread through just about every nook and cranny in the mold.

I also poured a switch frog. Usually I have trouble extracting the pattern without disturbing the rails. This time I set the pattern in a core box, made a core and poured it that way. I attached a photo of the core box, core print, core and casting, it's a good alternative way to pour patterns with delicate details.
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jscarmozza
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Re: Advice on pouring thin sections

Post by jscarmozza » Sun Jan 22, 2017 2:49 pm

I forgot to thank Big Dave and OddDuck for their advice, couldn't have done it without out you guys. Thanks, John

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steamin10
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Re: Advice on pouring thin sections

Post by steamin10 » Sun Jan 22, 2017 6:13 pm

Now that you have gone down the trail, you have stepped forward from those that wish, and those that do.

I am happy for you, that some of the results are satisfying. It was by you r hand and understnading. I cant wait to see your next project. Now that you are all together and running, it is easy to continue.

So whats next...
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

jscarmozza
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Re: Advice on pouring thin sections

Post by jscarmozza » Mon Jan 23, 2017 8:53 am

Unfortunately, 'what's next' may be painting the kitchen.

I cleaned up the casting after supper yesterday, I guess didn't get the core centered properly as one side is about 1/16" thicker than the other; not the end of the world because it's the edges I left long with the intention to trim. One thing I didn't mention was the result of pouring through the cores. I made up a core wash of molasses water and graphite as per Ammen's instructions and coated the inside of the sprues, runners and top of the cores. I think it worked, the cores remained pretty solid and were only burned out about 1/2" deep where they were in contact with the metal, and the finish on the sprue and runners was better than the casting. However, I think that is because of the lower pouring temperature of aluminum, I don't think pouring through a core, with or without a wash, would work with brass or iron as the high temperature would burn out the core before the pour was complete and wash sand into the casting. John

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steamin10
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Re: Advice on pouring thin sections

Post by steamin10 » Mon Jan 23, 2017 2:58 pm

I have but dismal experience with iron, as its heat is destructive to crucible and furnace, due to long heating times.

Brass and bronzes may skin and actually flow into the sand , giving you a cavity surrounded by sand filled metal. very displeasing. Scabbing is similar, and is all in the wrong sand mix. Aluminum is easy by comparison, and washes can make the casting very slick. You have now seen that..

Washing of loose sand is the bane of casting, and to be avoided, as otherwise good castings will have acne from loose grains settling here and there. I use talcum powder and sugar water or corn stach for a light spray on the cope and drag to seal pretty castings.

Big foundries use alchohol based washes that are set afire just before close up to set them dry, and serve the same purpose to slick the pattern surface.

All in all, one cast is worth ten thousand words. Nothing teaches the workings than a measured experience. Good on ya.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

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